Tube forming



Jan. 6, 1970 o, EDSTRQM ETAL 3,487,675

TUBE FORMING Filed May 25, 1966 3 Sheets-Sheet l INVENTORS. JOHN OLOF EDSTROM SVEN ERIC INNERMAN BENGT HENRIK BERG BRIAN EDWARD MILLS iwgm TTORNE Y5.

Jan. 6,1970 J. o. EDSTROM ETA!- 3,437675 TUBE FORMING Filed May 25, 1966 I 3 Sheets-Sheet '8 Fig.3

INVENTORS,

N OLOF EDSTROM N ERIC INNERMAN BENGT HENRIK BERG BRIAN EDWARD MILLS Jan. 6, 1970 J, o, gum-Rd ET AL 3,487.375.

TUBE FORMING Filed May 25. 1966 V 3 Shuts-Shut I Fig.5

INVENTOR:

JOHN OLOF EDSTROM SVEN ERIC INNERMAN BENGT HENRIK BERG BY BRIAN EDWARD MILLS United States Patent 3,487,675 TUBE FORMING John Olof Edstrom, Sven Eric Innerman, Bengt Henrik Berg, and Brian Edward Mills, Sandviken, Sweden, assignors t0 Sandvikens Jernverks Aktiebolag, Sandviken, Sweden, a corporation of Sweden Filed May 25, 1966, Ser. No. 552,766 Claims priority, application Sweden, Feb. 1, 1966, 1,242/66; Feb. 10, 1966, 1,668/66 Int. Cl. B21b 17/02 US. Cl. 72-370 9 Claims ABSTRACT OF THE DISCLOSURE A method and machine are disclosed for producing tubes of zirconium and zirconium base alloys. In the normal utilization of such tubes hydride inclusions may be formed which tend to weaken the tube walls if they extend radially of the axis of the tube. The tubes formed in accordance with the present invention have the char acteristic that such hydride inclusions are substantially parallel to the inner and outer tube surfaces. Hence, any reduction in tube strength is minimal. The machine and method are also applicable to producing tubes of other metals. There is also a disclosure of tubes formed of zirconium and zirconium base alloys having specific characteristics.

This invention relates to the production of tubes of zirconium and zirconium-base alloys. Particularly, the invention is applicable to zirconium and to Zircaloy alloys which consist of zirconium with additions of, for example, one or more of the following: tin, iron, nickel, chromium, and columbium. Such alloys may also contain minor quantities of other elements, such as molybdenum or copper.

Tubes of zirconium and zirconium-base alloys are use for example, in the nuclear industry. Often during manufacture, such tubes are subjected to an autoclave treatment to create a protective layer of oxide. 'During that treatmen or during use, hydrogen may be absorbed into the metal in sufficient quantity to cause precipitation of hydrides to form inclusions in the form of platelets throughout the metal. It is known that the manner or type of the cold working can determine the direction of the orientation of the platelets which form later. The direction of the orientation is of substantial importance during use of the tubes. If the orientation is radial, that is, from the outside surface toward the inside surface, there is a tendency for radial cracks to form which may result in leakage through the tube wall. If the orientation is parallel to the inner and outer tube surfaces, the problem of such cracks and resulting leakage is minimized or rendered negligible. In general, the orientation is perpendicular to the general lines of the compression forces to which the metal has been subjected, and is parallel to the prior tensile forces.

It is an object of the present invention to produce tubes of zirconium and zirconium-base alloys wherein there is cold working which is such that any hydride inclusions which form are not oriented radially with respect to the axis of the tubes. It is a further object to provide for cold working zirconium and zirconium-base alloy in such a way as to insure that such hydride inclusions are oriented somewhat parallel to the tube surfaces. It is a further object to provide tubes of the above type which are superior to the prior similar tubes. It is a further object to provide for the above with apparatus which is eflicient and dependable in use, and which is relatively simple in construction. These and other objects will be in part obvious and in part pointed out below.

In accordance with the present invention, tubes of zirconium and zirconium-base alloys are cold-worked to predetermined dimensions by a carefully controlled reduction in the wall thickness. This reduction insures a satisfactory orientation of hydride inclusions which appear later in the material.

In carrying out the invention, tubes having a wall thickness greater than that desired in the finished tubes are cold worked upon a pilger mill which is unique in its construction and mode of operation. That pilger mill and its mode of cold working various metals is disclosed in another application which will be co-pending with this present application and which is related to Swedish patent application No. 1668/66, filed Feb. 10, 1966.

in the drawings:

FIGURE 1 is a vertical section of a pilger mill illustrating one embodiment of the invention;

FIGURE 2 is an enlarged view of the mill rolls shown at the left in FIGURE 1;

FIGURE 3 is a plan view of the tube working groove on the face of one of the rolls of FIGURE 2;

FIGURE 4 is a sectional view upon a somewhat larger scale and showing the roll grooves on the line 44 of FIGURE 2;

FIGURE 5 is an enlarged view with the lower portion in section of the chuck of FIGURE 1 which holds the workpiece; and,

FIGURE 6 is a diagram illustrating the critical relationship which is involved in cold-working the tubes in accordance with the present invention.

Referring to FIGURE 1 of the drawings, a pilger mill is shown having a mill stand 10 with a pair of rolls 11 and 12 mounted respectively upon shafts 13 and 14. Rolls 11 and 12 have grooves 15 and 16, respectively, for rolling tubular blanks, illustratively 18 and 18a, mounted upon a cylindrical mandrel 17. The mill stand is stationary, and while each blank is being cold-worked, it is moved back and forth between the rolls with a generally progressive movement of the blank from right to left. That is, each movement of the blank to the left is more advanced than the prior movement to the left. The rolls rotate at the same speed in opposite directions, as shown by arrows, so that they move together toward the right within the zone at 33 where they engage the tube. Each of the grooves 15 and 16 in the rolls is substantially semi-cylindrical (see FIGURE 4) in cross-section throughout, but of varying Widths or diameters, as illustrated in FIGURE 3. That is, each of the grooves has a tapered reducing portion 30 within which the tube is worked or reduced, a finishing portion 31 which is of the diameter of the finished tube, and a relief portion 32 which is of a uniform diameter which is slightly greater than that of the tubular blank prior to the cold-working operation. The leading end of the tapered reducing portion 30 extends from the trailing end of the relief portion and is of the same diameter, and the finishing portion extends from the trailing end of the tapered reducing portion and is of the same diameter. The grooves on the rolls lie mirror-symmetrical (FIG- URES 1 and 2) with respect to the point of tangency at zone 33 between the rolls.

During operation, the tubular blank which is being reduced is supported and moved back and forth by an assembly upon a carriage 50 which is slid-ably sup-ported upon a base 51, and which is moved along the base by the rotation of a screw shaft 52. A cam drum 53 is rotatably mounted in carriage 50 and has a cam groove 54 which is a continuous or loop groove, the portion on the far side of the drum being identical with that shown on the near side. Extending through a slot in the top of the casing of carriage 50 is a cam follower 59 which is rigidly mounted in a chuck holder 63 of a chuck assembly 57. Rotatably 3 mounted in chuck holder 63 is a chuck 62 which is adapted to clamp rigidly a tubular blank 18a and the mandrel 17.

Drum 53 is rotated synchronously with rolls 11 and 12 by a drive assembly extending from the mill stand and represented by a gear 56, a mating gear and a spline shaft 55. This drive provides the continuous back and forth movement of the tubular blanks and it also drives the carriage 50 by screw shaft 52 progressively toward the mill stand from a position to the right of that shown so that the tubular blanks are fed a distance at least as great as their original length.

Each rotation of drum 53 moves the chuck assembly through a back and forth oscillation in which the blanks on mandrel 17 are first moved axially to the left through an advance stroke from somewhat the position shown in FIGURE 1 to that of FIGURE 2. The assembly is then moved back through a return stroke during which a blank is worked. That is, the blank reducing and finishing take place only during the return stroke, the advance stroke being only to position a blank for the working.

The synchronized rotation of rolls 11 and 12 and drum 53 causes the blank to be engaged by the tapered reducing portions 30 (FIGURE 3) of the rolls at the start of the return stroke. At that time the blank is moving to the right from the position of FIGURE 2. The tubular blank is then engaged by the finishing portions 31 of the grooves during the remainder of the return stroke toward the right. The relief portions 32 of the grooves then move past the blank during the entire advance stroke to the position of FIGURE 2. In general, the rate of movement of the chuck holder is determined by the shape of groove 54 in drum 53. However, at the beginning of the return stroke, the blank is accelerated to the speed of the rolls at the mean radii of the groove portions 30 and 31. When the blank has been gripped or clamped by the rolls there is no relative axial movement between the interengaged surfaces of the blank and the rolls. Hence, in fact, the rolls control the movement of the blank and the shape of groove 54 is such as to correspond with that rate of blank movement.

As indicated above, simultaneously with this oscillating movement of the tubular blanks, carriage 50 is moved at a slow constant rate toward the mill stand by screw shaft 52 which is driven by a gear assembly not shown. This causes the above-mentioned progressive movement of the tubular blanks toward the left during each back and forth movement of the blanks. Hence, when the leading ends of the tapered reducing portions 30 of the grooves approach a blank, there is an advanced portion of the unworked blank within the working zone 33 (FIGURE 2). That advanced portion of the tubular blank is engaged and compressed against the mandrel by the action of the tapered portions of the grooves, and a bulge or wave of metal is produced at the left of line 4-4 in FIGURE 2. The relationships and synchronous movements are such that the mandrel and the blank are then moving to the right at substantially the speed of the groove portions 30 of the rolls. Hence, the bulge or wave of metal is rolled relatively toward the left on the mandrel, thus to reduce the wall thickness and to produce a correspondingly increased length of the blank or tube. A tapered portion of the tubular blank remains between the original tube blank portion and the fully-reduced tube portion, although in effect a portion of the tubular blank at the working zone 33 is reduced from its original size to substantially it final size in one step with axial flow of the metal, i.e., the metal flows parallel to the cylindrical surfaces of the tube. The tubular blank continues its return movement, the bulge or wave of metal being flattened out by the finishing portions 31 of the grooves. The entire reducing and finishing operation is carried on while the cam follower 59 is moving in a portion of groove 54 having a constant or approximately constant pitch. Hence, the blank moves at the rate of the rolls at the mean radii of the groove portions 30 and 31 so that there is a pure rolling action.

Referring now to FIGURE 4, each of the grooves and 16 has its side edges beveled at 34 so that the cavity formed by the mating grooves has two diametrically-spaced deviations from the true circular cross-section shape. Hence, the initial action of grooves 15 and 16 is to produce protrusions on the opposite sides of the tubular blank having the configuration of the beveled edge surfaces of the grooves. Between each two successive periods or cycles when the tubular blank is being reduced by the rolls, chuck 62 and the tubular blank are turned (see arrow 60) through an arc of the order of slightly less than This turning movement is produced by a ratchet assembly (not shown) which is enclosed within carriage 50 and is driven from spline shaft 61 (FIGURE 1). The ratchet assembly turns a spline shaft 61 upon which there is slidingly mounted a gear which meshes with a gear in the chuck holder 63 through which the turning movement is transmitted to the chuck.

As a result of this step-by-step turning movement, the protrusions which start to form on the tubular blank during one cycle are turned prior to the next cycle toward the bottoms of the respective grooves 15 and 16 and the metal forming the protrusions is worked and caused to flow so that a true cylindrical form is produced. Each of the step-by-step turning movement is sufficiently less than 90 to avoid a pattern of the formation of the protrusions in axially aligned zones, and to insure that each portion of the tube is cold worked and finished uniformly.

With the cooperating roll grooves and the synchronized movements discussed above, there is no sharp break in the tube surfaces which would cause flaws in the finished product. The rounded surfaces 34 and the turning movement avoid the tendency for the metal at the sides to be formed into fins. The pressures which cause the flow of the metal are uniform and equally distributed.

Chuck assembly 57 is constructed to permit relative movement between chuck 62 and chuck holder 63 so that the chuck may turn about its axis as discussed above, and it may also move axially to the right with respect to the chuck holder. To permit the axial movement (FIG- URE 5), chuck holder 63 has a sleeve extension 64, at the end of which there is a flange 65 which snugly engages the inner surface of the shell of chuck 62, The shell of chuck 62 has a removable flange 66 which overlies flange 65 and snugly engages the outer surface of the sleeve extension 64 of the chuck holder. Chuck 62 has a plurality of cavities within which the same number of springs 67 are respectively positioned, and each spring has an aligning pin 67a which is mounted on flange 65. Springs 67 are under compression so that they push at the right against flange 65 and at the left against the chuck wall so as to resiliently urge the chuck to the left. Two ring gaskets 68 and 69 assist in insuring dampened and smooth axial movement of the chuck with respect to the chuck holder. A vent opening 70 is provided for the passage of air to and from the space between flanges 65 and 66.

The resilient mounting for the chuck permits the axial movement of mandrel 17 and the tubular blanks with respect to the chuck holder. Referring to FIGURE 2, when a tubular blank is being reduced by the action of the rolls, the rolls exert substantially pressures upon the tubular blank axially to the right. Springs 67 are sufl iciently strong to hold the tubular blanks in the proper operating relationship. However, the springs permit relative movement whenever the axial forces exerted upon the tubular blank by the rolls exceed a predetermined value. This resilient mounting permits rolling tubular blanks having different diameters and different rates of reduction than would be possible theoretically for a particular configuration of groove 54 on a drum 53.

In order to obtain the relatively high reduction in the tube wall thickness in one step, as is contemplated with the invention, the reducing portion 30 of the groove in each of the rolls should have a relatively long taper. Illustratively, the Wide end of reducing portion 30 is inclined at an angle of the order of 5 to 8 from. the pitch circle, and the invention contemplates that this should be within the range of 4 to The term pitch circle, as here used, means a circle concentric with the roll at the middle of the groove, and tangent to the similar circle of the other roll. As the mandrel is cylindrical, the angle between the mandrel surface and the axis of the outer surface of the tube corresponds to the taper of the roll groove. At its leading or larger end the diameter of the reducing portion 30 of the groove is somewhat greater than that of the original tubular blank. The reducing portion 30 of the groove is in accordance with the following formula:

Y =Y bx in which Y is the wall thickness of the blank, Y is the reduced wall thickness in a section 11, x is the distance along the tube axis of the section n from the unreduced blank, and b is a constant, determined for each set of conditions,

In this embodiment the radial extent of the various portions of each of the grooves in rolls and 16 is as follows: the reducing portion 30 extends 60; the finishing portion 31 extends 40; and, the relief portion 32 extends 260. The extent or relative length of each of the portions of the grooves varies with different operating conditions, such as the size and wall thickness and the characteristics of the metal. In general the portions 30 and 31 do not extend more than 180, and preferably extend between 100 and 150. The finishing portion 31 of each of the grooves has sufficient length to perform its finishing operation during each cycle upon a length of the tube which is several times the length of the finished tube which is produced by a single metal-working cycle. Hence, during each cycle, the length of the tubular blank which is fed to the zone 33 is reduced by the reducing portions 30 of the grooves so that the tube fits the mandrel snugly. During subsequent cycles that portion of the tube is subjected to repeated finishing operations by the finishing portions 31 of the grooves, and the internal diameter of the tube is increased so that the tube is readily removed from the mandrel.

Mandrel 17 is of sufficient length to retain two of the blanks. Hence, as shown in FIGURES l and 2, the trailing end of one tubular blank 18 is finished simultaneously with the starting of the cold-working of the next tubular blank. In that way, the ends of the tubular blanks are finished without scrap losses.

It has been indicated above that the diameter of mandrel 17 is substantially that of the internal diameter of the tubular blanks. Hence, there can be little or no reduction in the internal diameter of the tube, and the reduction in wall thickness constitutes substantially the entire cold-working. In general, the wall thickness of the tubular blanks is of the order of .2 to .25 of the external diameter, and the external diameter is less than the order of 50 mm. Illustratively, a tubular blank of the dimensions 34 x 7 mm. (external diameter of 34 mm. and a wall thickness of 7 mm.) was rolled to the dimensions of 19 x 1.5 mm. in one instance, and to 19 x .75 mm. in another instance. These represent reductions in the crosssectional area of the metal of the order of 87% and 93%, respectively. Illustratively, the diameter of rolls 11 and 12 is of the order of 500 mm. or less, for example, 150 to 350 mm. The rate of feed in the above example for each rolling or cold-working cycle 'was of the order of .5 to 4.5 mm., preferably 1 mm. to 2 mm.

It has been indicated above that the pilger mill shown in the drawings and the process described may be used to cold-work tubular blanks of various metals, such as carbon steel, low-alloyed steel, high-alloyed steel and other metals. However, the invention of the present application is set forth in relation to zirconium and zirconiumbase alloys. As explained above, tubes of zirconium and zirconium-base alloys have been produced and 6 used in such a way as to cause hydride inclusions to form within the metal, and that the present invention permits the control of the orientation of such inclusions. Specifically, the inclusions are oriented to lie generally parallel to the tube surface, rather than radially of the tube.

According to this invention, the rolling operation produces satisfactory finished tubes if the Q factor in the following formula is relatively high and has a value of the order discussed more fully below:

where F(t) is the change in the wall thickness of the tubular blank,

t is the original wall thickness,

1 is the wall thickness after rolling;

F(D) is the change in the mean diameter of the tubular blank,

D isd the mean diameter of the original tubular blank,

D is the mean diameter of the tubular blank after rolling.

The Q factor also may be defined as the ratio between the percentage of change in the wall thickness and the percentage of change in the mean diameter of the tube. It is understood that each of the percentages is calculated by dividing the change in the dimension by the original dimension. In general very satisfatcory tubes of zirconium and zirconium-base alloys have been produced by reducing the tubular blanks as described above, so as to maintain a Q factor of the order of 1.0 or more, and preferably greater than 2, provided there is a reduction in the cross-sectional area of the metal of not less than 50% and commercially of the range of 75% to 95%, often to Under some circumstances, the rolling may be performed in more than one step. The tubes may be subjected to additional working or other processing without departing from the scope of the invention.

FIGURE 6 of the drawings shows various Q factors with the reduction rate R being the percentage in the reduction of the cross-sectional area of the metal. The orientation angle of the hydride inclusions with respect to the radius of the tube represents the vertical axis of the diagram. It is recognized that the percentage reduction must be something less than The curves show that a high Q factor gives excellent results, but that a low Q factor produces unsatisfactory orientation of the inclusions. In one particular mode of practicing the present invention, a Zircaloy tubular blank was cold-worked, which was originally 24.5 x 4.25 mm. After rolling the tubular blank was 16 x .76 mm. Hence, the mean diameter was changed from 20.25 mm. to 15.24 mm., with a reduction in the cross-section area of the metal of 86%. In accordance with the formula discussed above, the Q factor is calculated to be 3.3.

In another instance, a tube having an external diameter of 19.05 mm. and a wall thickness of 2.78 mm. was reduced to an external diameter of 13.91 mm. and a wall thickness of .68 mm. During this reduction the Q factor was 4 and the cross-sectional area was reduced 80%. At the start of the working or reducing, the internal diameter of the tube was reduced so as to fit the mandrel snugly, the snug fit being apparent at 4.52 mm. from the adjacent end of the unworked portion of the tubular blank. The reducing grooves were 40 mm. in length, and the finishing grooves were 220 mm. in length. The finishing operations occurred 40 to 50 times upon each portion of the tube before that portion passed beyond the finishing zone.

During the finishing operations, the metal displaced at the edges of the grooves and tending to form protrusions was worked, with the result that the tube diameter was enlarged slightly to cause the completely finished tube to move freely from the mandrel. At all times the roll surfaces contacting the tubes or tubular blanks move toward the chuck. Hence, in FIGURES 1 and 2 tubular blank 18 is urged to the right against the solid support provided by tubular blank 18-a which is clamped in the chuck. Therefore, there is no tendency for the finished tube to be projected from the mandrel by the action of the rolls.

The above description includes explanations of the extremely important improved properties of zirconium and zirconium-base alloy tubes produced in accordance with the present invention. However, it may be that the reasons for all of the desirable results are not fully understood and are not apparent. However, the invention as set forth in the following claims accomplishes the objects set forth above.

What is claimed is:

1. In the method of producing tubes of zirconium and of zirconium-base alloys which may be subjected to ambient conditions which will produce hydride inclusions within the tube walls and it is desirable to insure that such hydride inclusions will have an orientation which is generally tangential or parallel to the tube surfaces and wherein the finished tubes have predetermined diameter and wall thickness characteristics, the steps of, producing an original tube having a wall thickness which is at least twice the wall thickness of the tube being produced and which has an inner diameter which is substantially that of the tube being produced, and milling the tube by a single step to produce a reduction in wall thickness of not less than 50% by subjecting it to compression forces against a mandrel and produced by a pair of rolls have matching 7 slots which form a cavity which is substantially circular in cross-section and which is tapered from substantially the diameter of the original tube to that of the tube which is being produced, and wherein there is a ratio of not less than one between the percentage change in wall thickness and the percentage change in mean diameter.

2. The method as described in claim 1 wherein the mandrel substantially fills the bore of the tube.

3. The method as described in claim 1 wherein the tube is subjected to a subsequent finishing step.

4. The method as described in claim 1 wherein the original tube has a wall thickness of the order of .2 to .25 of the external diameter of the tube and wherein said external diameter is less than 50 mm.

5. The method as described in claim 1 wherein the rolling step produces a reduction in wall thickness within the range of 75% to 95% in a single step.

6. The method as described in claim 1 wherein said milling is performed by a pair of matching rolls with mating grooves with a tapered portion which is inclined from the pitch circle within the range of 4 to 7. The method as described in claim 1 wherein said mandrel is cylindrical.

i 8. In the method of producing tubes of zirconium and of zirconium-base alloys which may be subjected to ambient conditions which will produce hydride inclusions within the tube walls and it is desirable to insure that such hydride inclusions will have an orientation which is generally tangential or parallel to the tube surfaces and wherein the finished tubes have predetermined diameter and wall thickness characteristics, said producing being from an original tube having a wall thickness which is at least twice the wall thickness of the tube being produced, the steps of, moving an advanced portion of said original tube into a forming zone upon a mandrel which substantially fills the opening in the center of the tube, milling said advanced portion by subjecting it to compressive forces against the mandrel by a pair of rolls having matching slots which form at their nip a substantially circular zone and which have mating tapered portions with the taper extending from a maximum diameter where the rolls first engage the tube which is substantially the external diameter of the original tube and a minimum diameter which is not greater than the mean diameter of the original tube, said rolls being rotated with their peripheries moving counter to the direction in which the advance portion is moved toward said zone and said taper decreasing in trailing relationship to the direction of movement of said tapered portions, moving said original tube and mandrel with said tapered portions at a rate to avoid substantial relative movement between said advanced portion and said tapered portions whereby a wave of metal is produced which flows substantially axially of said mandrel with a reduction in tube wall thickness of the order of to of the wall thickness of the original tube and with the inner diameter being reduced substantially to cause the reduced tube portion to tightly engage the mandrel, moving the tube and mandrel through a second advance step with the next adjacent portion of the original tube constituting the advance portion, repeating the milling step and performing a finishing step on the reduced tube portion to increase its internal diameter sufliciently to release it from the mandrel, and repeating the steps until the entire original tube is reduced.

9. The method as described in claim 8 wherein said mandrel is cylindrical.

References Cited UNITED STATES PATENTS 545,513 9/ 1895 Mannesmann 72-208 742,645 10/1903 Heer 72l93 1,980,186 11/1934 Coe 72-208 2,005,657 6/1935 Ludwig 72-193 3,342,648 9/1967 Zucker et al 29183 CHARLES W. LANHAM, Primary Examiner LOWELL A. LARSON, Assistant Examiner U.S. Cl. X.R. 72-700 

